In most cases, the jiggering method of the rotary profile tool type uses as the tool material a metal material, which is heated to produce a steam film between the tool and the plastic clay to be subjected to contact-rolling (referred to as jiggering), thereby preventing that plastic clay from sticking to the tool, while keeping smooth contact therebetween. (This method shall hereinafter be referred to as the heated tool method; see Japanese Patent Kokoku-Publication No. 30-6281 in this regard.) In other words, the prior art rotary profile tool type jiggering method, as referred to just above, involves heating (to about 100.degree. C.) a jiggering profile tool (roller) formed of an iron or aluminium material by cutting by means of a gas burner, an electric heater or the like to subject plastic clay to jiggering, while a steam film is produced between the tool and the plastic clay.
Japanese Patent Kokai Publication No. 56-75812 discloses a jiggering process wherein a thin gas film is produced either by rotating the gypsum mold at a high speed such that a gas film is produced at the contact area between the rotary jiggering profile tool and the plastic clay, or by blowing a gas to the contact area. The high speed rotation of the gypsum mold is about at a doubled speed (e.g., 900-1200 rpm) of the usual rotational speed (450-600 rpm for coffee or tea cups). Preferably, the rotary jiggering profile tool is rotated approximately about the same speed as the mold for producing the thin gas film.